If the color levels of a pixel are arranged one behind the other, then the chambers must be made of a clear transparent material and the colored liquid must be transparent. Furthermore, a white or silvery white reflective layer must be arranged behind the color levels if it is a direct-light display.
If the color levels of a pixel are arranged side by side in a direct-light display, the bottom of the color level may be white or black and—if the color level is made of a clear transparent material—a white or black surface may be arranged behind the color levels, so the color level appears white or black when filled with the clear colorless transparent medium.
In the square design, the pixels and their color levels have an edge length of less than 3 mm and a volume of less than 0.5 mm3. The colored liquid may be conveyed into the color levels by micropumps, piezoactuators, electrowetting, or compressed gas. If the color levels of a pixel are arranged one behind the other, then the colors are mixed subtractively by using the three secondary colors cyan, magenta, and yellow. These colors act as filters, with cyan filtering the primary color red out of white light and magenta filtering the primary color green out of white light, while yellow filters the primary color blue out of white light. If the three filters cyan, magenta, and yellow are stacked one above the other, then the three primary colors red, green, and blue and thus the light are filtered out, so the pixel appears black.
Mixing of color by subtractive and additive methods as well as display units of the type defined above are known from the patents EP 1 090 384, U.S. Pat. No. 6,037,955, and U.S. Pat. No. 6,747,777.
Although it is theoretically possible to produce all colors by mixing primary colors or secondary colors, in practice it is extremely difficult visually and in terms of control technology to produce the optimal hue and the correct color intensity in relatively small color levels and pixels and to do so in direct light, which is often variable.
Accordingly, it would be desirable to provide a method with which mixing of colors is facilitated.